PHYSICS LESSON NOTE FOR SS2 THIRD TERM:

Topic: Lens

What Are Lenses

Lenses are optical devices that are used to bend or refract light in order to focus it or to form an image. They are used in many different applications, such as eyeglasses, microscopes, cameras, and telescopes.

Types of Lenses:

There are two main types of lenses:

Converging lenses 

Diverging lenses.

1. Converging lenses: These lenses are thicker in the middle than at the edges and are also known as convex lenses. They cause parallel rays of light to converge at a point known as the focal point. Converging lenses are commonly used in magnifying glasses, cameras, and telescopes.
2. Diverging lenses: These lenses are thinner in the middle than at the edges and are also known as concave lenses. They cause parallel rays of light to diverge and appear to come from a point known as the virtual focal point. Diverging lenses are commonly used in eyeglasses and projectors.

Focal Length and Power of a Lens:

The focal length of a lens is the distance between the lens and the focal point. It is denoted by the symbol “f” and is measured in meters (m). The power of a lens is a measure of its ability to bend light and is defined as the reciprocal of the focal length, denoted by “P” and measured in diopters (D).

P = 1/f

Image Formation by Lenses:

When light passes through a lens, it can form either a real image or a virtual image.

1. Real image: A real image is formed when the light rays converge to a point after passing through the lens. This image can be projected onto a screen and is inverted. Converging lenses can form real images.
2. Virtual image: A virtual image is formed when the light rays appear to converge to a point behind the lens. This image cannot be projected onto a screen and is upright. Diverging lenses can form virtual images.

Applications of Lenses:

1. Eyeglasses: Lenses are used in eyeglasses to correct vision problems.
2. Cameras: Lenses are used in cameras to focus light and form an image on a film or digital sensor.
3. Microscopes: Lenses are used in microscopes to magnify small objects.
4. Telescopes: Lenses are used in telescopes to collect and focus light from distant objects.

Lenses are important optical devices that are used in many different applications. Understanding the types of lenses, their focal length and power, and how they form images can be useful in designing and using these devices.